Add all compatible system types directory to module paths

fixes #12915
closes #12916

Since Spack has support for specific targets it might happen that
software is built for targets that are not exactly the host because
it was either an explicit user request or the compiler being used is
too old to support the host.

Modules for different targets are written into different directories
and by default Spack was adding to MODULEPATH only the directory
corresponding to the current host. This PR modifies this behavior to
add all the directories that are **compatible** with the current host.

2 files changed, 14 insertions, 1 deletions

diff --git a/lib/spack/spack/architecture.py b/lib/spack/spack/architecture.py
index c67b63cba0..53cbc44ca5 100644
--- a/lib/spack/spack/architecture.py
+++ b/lib/spack/spack/architecture.py
@@ -493,3 +493,15 @@ def sys_type():
     """
     arch = Arch(platform(), 'default_os', 'default_target')
     return str(arch)
+
+
+@memoized
+def compatible_sys_types():
+    """Returns a list of all the systypes compatible with the current host."""
+    compatible_archs = []
+    current_host = cpu.host()
+    compatible_targets = [current_host] + current_host.ancestors
+    for target in compatible_targets:
+        arch = Arch(platform(), 'default_os', target)
+        compatible_archs.append(str(arch))
+    return compatible_archs
diff --git a/lib/spack/spack/main.py b/lib/spack/spack/main.py
index a2220a9ba8..c3746b6b26 100644
--- a/lib/spack/spack/main.py
+++ b/lib/spack/spack/main.py
@@ -585,7 +585,8 @@ def print_setup_info(*info):
 
     # print sys type
     shell_set('_sp_sys_type', spack.architecture.sys_type())
-
+    shell_set('_sp_compatible_sys_types',
+              ':'.join(spack.architecture.compatible_sys_types()))
     # print roots for all module systems
     module_roots = spack.config.get('config:module_roots')
     module_to_roots = {